The polymerization of isobutylene using Friedel-Crafts type catalysts, such as BF3, is a generally known procedure which is disclosed, for example, in “HIGH POLYMERS”, Vol. XXIV (J. Wiley & Sons, Inc., New York, 1971), pp. 713 ff. Reference is also made Fujisawa et al, Japan Kokai Tokkyo Koho (1994) JP 06345821 A; Faurh et al, Ger. Offen (1994) DE 4231748; Fujisawa et al, Japan Kokai Tokkyo Koho (1993) JP 05186513 A; Kuznetsova et al, U.S.S.R. (1991) SU 1659424 A1; Noda et al, European Patent Application (1991) EP 452875; Noda et al, Japan Kokai Tokkyo Koho (1988) JP 63205305 A; Sangalov et al, (1983) SU 1016304 A1; Prokofev et al, Promyshehlennost Sinteticheskogo Kauchuka (1982) Vol. 7, 12-15; Rooney, J. Applied Polymer Sci. (1980) Vol. 25(7), 1365-1372; Byrikhin et al, Lomonosova (1975) Vol. 5(2) 107-112; Priola, Makromolekulare Chemie (1975) Vol. 176(7), 1969-1981; U.S. Pat. No. 3,721,661; Steigerwald, DE 2118869; and Penfold et al, Proc. Of the Chem. Soc. (London) (1961) 311-312. The degree of polymerization of the products obtained in these processes varies according to which polymerization technique is used. In this connection, it is to be understood that the molecular weight of the polymeric product is directly related to the degree of polymerization.
It is also known that PIB may be manufactured in at least two different grades—regular and high vinylidene. Regular grade PIB may range in molecular weight from 500 to 1,000,000 or higher, and is generally prepared in a batch process at low temperature, sometimes as low as −50 to −70° C. AlCl3 or modified AlCl3 is used as catalyst. The catalyst is not totally removed from the final PIB product. Molecular weight may be controlled by temperature since the molecular weight of the product varies inversely with temperature. Higher temperatures lead to lower molecular weights. Reaction times are often in the order of hours. The desired polymeric product has a single double bond per molecule, and the double bonds are mostly internal. Generally speaking, at least about 90% of the double bonds are internal and less than 10% of the double bonds are in a terminal position. Even though the formation of terminal double bonds is believed to be kinetically favored, the long reaction times and the fact that the catalyst is not totally removed, both favor the rearrangement of the molecule so that the more thermodynamically favored internal double bond isomers are formed. Regular PIB may be used as a viscosity modifier, particularly in lube oils, as a thickener, and as a tackifier for plastic films and adhesives. PIB can also be functionalized to produce intermediates for the manufacture of detergents and dispersants for fuels and lube oils.
High vinylidene PIB is characterized by a large percentage of terminal double bonds, typically greater than 70% and preferentially greater than 80%. This provides a more reactive product, compared to regular PIB, and hence this product is also referred to as highly reactive PIB. The terms highly reactive (HR-PIB) and high vinylidene (HV-PIB) are synonymous. The basic processes for producing HV-PIB include a reactor system, employing BF3 and/or modified BF3 catalysts, such that the reaction time can be closely controlled and the catalyst can be immediately neutralized once the desired product has been formed. U.S. Pat. No. 5,068,490 describes a process for preparing highly reactive polyisobutylene using BF3 etherate complex as the catalyst.
Since formation of terminal double bonds is kinetically favored, short reactions times favor high vinylidene levels. The reaction is quenched, usually with an aqueous base solution, such as, for example, NH4OH, before significant isomerization to internal double bonds can take place. Number average molecular weights (Mn) of about 950-1050 is the most common product. Conversions, based on isobutylene, are kept at 75-85%, since attempting to drive the reaction to higher conversions reduces the vinylidene content through isomerization.
While such conventional processes provide good yields of high molecular weight PIB, it is quite difficult to consistently obtain molecular weights (Mn) in the low numbers such as, for example, under 1000. It is still more difficult to obtain even lower, e.g. under 800, or under 500, or even under 300 by using such processes. Attempts to produce PIB in the lower range (e.g., under Mn of 800) usually leads to loss of reactor control during production. The only option left with operators is to control the PIB reactors in manual mode i.e. switching the catalyst pumps to manual flow rather than using traditional feedback control to adjust catalyst flow sensing the reactor temperature. This usually leads to a difficult control situation and a high amount of ‘off-spec’ PIB product i.e. not meeting molecular weight, polydispersity or flash point constraints.
The usual method for controlling the molecular weight involves increasing the temperature of the reactor to a certain set point, and maintaining a constant chiller temperature. As reactor temperature increases, the ΔT between the reactor and the chiller temperature increases causing the conversion to increase. The higher the reactor temperature, the lower will be the molecular weight. The decrease in molecular weight can usually be attributed to a combination of chain transfer to monomer and termination reactions. A linear relationship is usually obtained when log Mn is plotted against the reciprocal of temperature (Arrhenius plot). At a constant chiller temperature, the following relationship holds:
  log  ⁢          ⁢      M    n    ⁢  α  ⁢          ⁢      1          T      r        ⁢  α  ⁢          ⁢      1    Conversion  Therefore temperature is the most important parameter in controlling molecular weight. The reactor temperature is controlled to the set point by employing feedback control i.e. by sensing the reactor temperature and then controlling the initiator feed rate to the reactors. For producing certain very low molecular weights (typically below 700 to 800 Mn), the reactor temperature set-points need to be set very high. The higher reactor temperatures result in conversions reaching 100% because of the large difference between reactor and chiller temperatures. At such a stage the usual feedback control logic of manipulating the initiator flow rate to control temperature does not hold. This results in a loss of control of the reaction making it very difficult to consistently produce low molecular weight PIB polymers within the desired specifications (Mn, PDI and viscosity and flash point).
U.S. Pat. No. 5,962,604 describes a process for preparing low molecular weight, highly reactive polyisobutylene using BF3 as the catalyst. The process is conducted in at least two stages.
U.S. Pat. No. 6,683,138 describes a process for preparing highly reactive polyisobutylene using BF3 as the catalyst.
U.S. Pat. No. 5,556,932 describes a process for preparing chlorine-free, non-drying isobutene-diene copolymers using BF3 as the catalyst.
EP 0154164 describes a process for preparing polyisobutylene using BF3 as the catalyst, ethylene as solvent and 2,4,4-trimethyl-1-pentene containing less than 1% by weight foreign constituents.
Highly reactive PIB oligomers with Mn under 1000 are useful as, for example, drilling fluid additives, precursors for specialty surfactants, viscosity modifiers and the like. It is, therefore, useful to find a manufacturing process to consistently obtain such oligomers without significant loss of control or economics.